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    <title>Document</title>
    <!-- <style>
        .box {
            background-color:lawngreen ;
        }
    </style> -->
</head>
<body>
    <div class="the_div">
    <p>我是p标签</p>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <a id="theA" href="#">我是一个a标签</a>
    <ul>
        <li>北京</li>
        <li>天津</li>
        <li>南京</li>
    </ul>
    <ol class="my_li">
        <li>大张</li>
        <li>大王</li>
        <li>大狗</li>
    </ol>
    <ul class="my_li">
        <li>小明</li>
        <li>小红</li>
        <li>小蓝</li>
    </ul>
</div>

<script>
    const a=document.querySelector('#theA')
    console.log(a);
    const h3=document.querySelectorAll('h3')
    console.log(h3);
    const li=document.querySelectorAll('li')
    console.log(li);
    const xiao=document.querySelectorAll('ul.my_li li')
    console.log(xiao);
    const xiaohong=document.querySelector('ul.my_li li:nth-child(2)')
    xiaohong.innerHTML=`小六`
    xiaohong.style.color='red'
    console.log(xiaohong);
    // const tianjin=document.querySelectorAll('li:nth-child(2)')
    // console.log(tianjin);
    const tianjin=document.querySelector('ul li:nth-child(2)')
    tianjin.classList.add('tianjin')
    tianjin.style.backgroundColor='lawngreen'
    console.log(tianjin);
</script>
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